The present invention relates to a measurement system and method for finding a position along a linear trackway. More particularly, the present invention relates to a measurement system and method for finding a position of a primary part of a linear motor with respect to a secondary part of the linear motor.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
For controlled operation of a three-phase synchronous linear motor, it is necessary to record the instantaneous commutation angle. The commutation angle is required in order to split the total current level required to develop a specific desired force correctly between the three phase currents. Furthermore, very exact position control is frequently required for linear motors. This is the case, for example, with machine tool drives. In applications such as these, the position signal is correspondingly also required to determine the current position of the primary part of the linear motor with respect to the secondary part of the linear motor.
German patent document DE 10 2005 017 498 A1 discloses a synchronous linear motor with contactless scanning of the tooth structure of a secondary part. The tooth structure of the secondary part, which has no permanent magnets and is in the form of a toothed rod, is designed to be position-dependent in the movement direction. The synchronous linear motor is equipped with an absolute position measurement system and with an incremental position measurement system, in such a way that the coarse resolution of the absolute measurement system is complemented by the fine resolution of the incremental measurement system.
To ensure clarity, in the following description a reference to a movement or position change in the context of the linear motor relates to a relative movement of some type between the primary part and the secondary part of the linear motor. This also applies for a movement of the primary part over the secondary part, or vice versa.
It would be desirable and advantageous to provide an improved measurement system which obviates prior art shortcomings and which is robust and in particular insensitive to dirt, for position finding.